Refining hydrocarbon oils



Patented June 7, 1949 UNITED STATES REFINING HYDROCARBON OILS Chicago, Ill., a corporati on of Indiana No Drawing. Application January 19, 194.6, Serial No. 642,426

. 6 Claims. 1

This invention relates to improvements in the refining of petroleum oils and more particularly to the refining of viscous petroleum oils, especially electrical insulating oils for use in transformers, oil circuit breakers and other electrical apparatus as insulating and/or cooling media which are noncorrosive to non-ferrous metals, particularly copper and silver.

Recent changes in construction material, and the severity of service of various types of equipment has been reflected in more drastic requirements in the properties of petroleum oils employed therefor. Petroleum oils refined by the usual methods heretofore employed, While considered in the past to be entirely satisfactory for their intended use, are now rejected because they fail to pass certain new specifications based upon newly developed equipment construction materials or upon more severe operating conditions for such equipment; as an illustration, a transformer oil refined by the usual process of sulfuric acid treating, neutralization and/or claying was considered satisfactory if it passed the dielectric strength test; now, however, there are severe copper and/or silver corrosion tests which such an oil will not meet.

It is an object of the present invention to provide an improved method of refining petroleum oils. Another object of the invention is to provide an improved method of refining viscous petroleum oil to produce a product substantially free of corrosive sulfur. Still another object of the invention is to provide an improved method of refining a petroleum electrical insulating oil to produce a product which is substantially free of polysulfides and which is noncorrosive to copper and/or silver. Other objects and advantages of the invention will become apparent from the following description thereof.

In accordance with the present invention, the foregoing objects can be attained by treating a petroleum oil, particularly a petroleum distillate containing mercaptans, with the required amount of concentrated sulfuric acid, preferably fuming sulfuric acid, neutralizing the acid treated oil with an excessive amount of a neutralizing agent and blowing or agitating the neutralized oil, preferably with air, at a sufiiciently elevated temperature to substantially dehydrate the oil without cracking, suitably at a temperature of from about 150 F. to about 220 F. for a time sufficient to substantially dehydrate said oil, preferably to a water content of less than about 0.1% by weight based on the weight of the oil treated. The neutralized oil is then washed with alcoholysteamed, blown bright and clay percolated to the desired color. The neutralizing agent is suitably an alkali metal hydroxide, preferably sodium hydroxide, and it is employed in amounts sufficient to provide an excess of alkali of from about 0.1% to about 1%, preferably about 0.5% by weight based upon the oil treated over that required to neutralize the acidity of the acid-treated oil. The neutralizing agent can suitably be used in an aqueous solution of any strength, for example, in concentrations in the range of from about 5% to about 30%, and preferably about 20% by weight. The acid-treated oil, prior to neutralization should not be airblown or otherwise treated to remove all of the sulfur dioxide resulting from the treatment of the oil with sulfuric acid. For the best results the sour oil should contain at least 0.05% and preferably from about 0.05% to about 0.5% sulfur dioxide, although the presence of greater amounts can be tolerated.

The herein-described invention will be better understood from the following examples which are given by way of illustration only and are not intended as limiting the scope of the invention:

Example Z.About 100,000 gallons of a transformer oil distillate having a Saybolt Universal viscosity at F. of about 55 seconds was treated at a temperature of about 60 F. to 100 F. with four pounds of 104 /2 54, sulfuric acid per gallon of distillate. The resultant sour oil, amounting to about 61,900 gallons, was transferred from an acid treater to a wash tank where it was neutralized with 4,500 pounds of aqueous caustic solution of about 23% strength. The amount of caustic solution used was equivalent to an excess of 0.6% of caustic based on the weight of the oil, the acidity of the sour oil being 5.7 milligrams of NaOH per gram of oil. While the caustic was being added to the sour oil, agitation was obtained by air blowing and by circulation through a pump. The temperature of the neutralized sour oil was raised to about 180 F. and maintained between 180 F. and about 220 F. for about 21 hours, at which time the water content was 0.08%. Agitation of the oil was then discontinued and the oil allowed to remain in a quiescent state for about 40 hours. The oil was then washed at a temperature of about F. to F. with 9,300 gallons of 60% alcohol. After removal of the alcohol extract, the oil was steamed to remove the 1%to 2% ofresidual alcohol in the oil. Water condensed during the steaming operation was withdrawn from the oil and the latter blown bright with air. The oil after percolation through clay to the desired color, was noncorrosive to copper and/or silver.

The noncorrosiveness of the finished oil was then demonstrated by subjecting it to the following corrosion test:

Copper and silver test strips, highly polished and thoroughly cleaned, were submerged in 100 cc. of the oil maintained at a temperature between 95 C. and 110 C. After 672 hours neither strip was corroded as evidenced by the absence of discoloration. Further evidence that the finished oil was substantiallyfree of corrosive sulfur was indicated by the following test:

The copper strip, after the 6'72 hours submersion, was freed of oil by rinsing with petroleum ether; after evaporation of the ether, the strip was treated with a few drops of fuming nitric acid and washed with a minimum amount of distilled water, the washings as well as nitric acid being caught in a beaker. To the solution about cc. of hydrochloric acid were added, the solution boiled to drive off free nitric acid and 5 cc. of barium chloride in a 10% solution then added to the beaker. The absence of a white precipitate at the end of six hours at 95 C. indicated the absence of sulfur or corrosive sulfur compounds. The foregoing method of determining the presence of free and corrosive sulfur in the finished oil is more fully described by the ASTM method D 117-43 set forth on page 188 of the ASTM Standards on Petroleum Products and Lubricants of September, 1943. While the ASTM test is applied only to copper, the silver :1:-

strip was added to the above test to demonstrate the noncorrosiveness to silver of the finished oil, which is required by certain special specifications.

A transformer oil finished by the method heretofore employed in the refining of such oil, in which excess caustic was not employed, and the water content of the neutralized oil not reduced in the manner hereinabove described, failed to pass the above described test as evidenced by discoloration of the test strips in less than 5 hours, and gave a positive polysulfide test.

, Example II.A transformer oil distillate was treated with four pounds of 104 /2 sulfuric acid in one pound dumps. The temperature of the oil at the time of each acid addition being about 60 F. and reaching a maximum temperature during the treating of about 96 F. The resultant sour oil was divided equally into two portions.

One portion was neutralized with caustic,

adding 0.6% excess caustic based on the oil. The oil was then blown in the steam bath with air for hour reaching a maximum temperature of about 150 F. The other portion was neutralized in the same manner as was the first portion, ex-

cept that the neutralized oil was blown for three 'hours at 200 F. followed by 16 hours at 180 F.

At the end of this time the oil was bright, indicating that substantially all of the water had been removed. Both portions were then finished identically by washing with 15 volumes of alcohol, steamed, blown bright and clay percclated to the same yield. The two portions of the oil were then submitted to the above described corrosion test with the following results:

The oil which was neutralized, but not heated at an elevated temperature for a time sufiicient to substantially dehydrate the oil, gave a questionable copper strip at the end of 11 hours and a definitely failing strip at the end of 21 hours. The

having a Saybolt Universal viscosity at other portion of the oil which was neutralized and treated to substantially dehydrate the oil gave a passing copper strip at the end of I20 hours. It is obvious from the foregoing examples that the treatment of the sour oil with an excess of the neutralizing agent and the substantial dehydration of the oil are essential to obtain a noncorrosive finished oil.

While the herein-described invention has been exemplified by reference to the transformer oils, it is not limited thereto, but is equally well adapted to the refining of petroleum oils in general, and particularly viscous petroleum oils, that is oils F. above about .50 seconds, such as turbine oils, spindle oils, combustion engine lubricants, technical white oils and the like.

The term concentrated sulfuric acid as used herein and in the appended claims means a sulfuric acid of at least about 95% strength and includes fuming sulfuric acid.

Therefore, while we have described our invention in connection with certain embodiments thereof, it is to be understood that these are by way of illustration only and are not intended to limit the scope of the invention, except insofar as the same is defined by the following claims.

We claim:

1. The method of refining a viscous petroleum oil comprising treating said oil with fuming sulfuric acid, treating the acid-treated oil containing at least about 0.05% sulfur dioxide with an alkali metal hydroxide in an amount in excess of that required to neutralize the acid-treated oil, air-blowing the neutralized oil in the presence of the excess neutralizing agent, in the absence of a diatomaceous filter-aid, at a temperature of from about F. to about 220 F., for a time sufficient to reduce the water content thereof to less than about 0.1%, and subsequently washing the dehydrated oil with alcohol, and treating said washed oil to remove substantially all of the alcohol therefrom.

2. The method of refining a viscous petroleum oil as described in claim 1, in which the alkali metal hydroxide is employed in amounts sufficient to provide from about 0.1% to about 1% excess alkali above that required to neutralize the acid-treated oil.

3. The method of refining a viscous petroleum oil to render the same noncorrosive to copper and silver comprising treating said oil with fuming sulfuric acid, treating the acid-treated oil containing from about 0.07% to about 0.5% sulfur dioxide with an alkali metal hydroxide in an amount of from about 0.1% to about 1% in excess of that required to neutralize the acid-treated oil and air-blowing the neutralized oil in the presence of excess alkali metal hydroxide and in the absence of a diatomaceous filter-aid at a temperature of from about 150 F. to about 220 F. for a time sumcient to dehydrate said oil to a water content of less than about 0.1%.

4. The process comprising treating a viscous petroleum oil with sulfuric acid of at least about 95% strength, neutralizing the acid-treated oil containing at least about 0.05% sulfur dioxide with an alkali metal hydroxide in an amount of from about 0.1% to about 1% in excess of that required to neutralize said acid-treated oil, air- 5 about 0.1%, and subsequently washing the neutralized, substantially dehydrated oil with alcohol, steaming to remove alcohol, and substantially dehydrating said alcohol-washed oil.

5. The method of refining a mercaptan-bearing petroleum oil comprising treating said oil with sulfuric acid of at least about 95% concentration, treating the acid-treated oil containing at least about 0.05% sulfur dioxide with an alkali metal hydroxide in an amount in excess of that required to neutralize the acid-treated oil, airblowing the neutralized oil in the presence of the excess neutralizing agent in the absence of a diatomaceous filter-aid, at a temperature of from about 150 F. to about 220 F., for a time sufficient to reduce the Water content thereof to less than about 0.1%, and subsequently washing the dehydrated oil with alcohol and drying the alcohol-Washed oil.

6. The method of refining a viscous petroleum oil comprising treating said oil with sulfuric acid of at least about 95% strength, treating the acidtreated oil containing at least about 0.05% sulfur dioxide with an alkali metal hydroxide in an amount in excess of that required to neutralize the acid-treated oil, air-blowing the neutralized oil, in the presence of the excess neutralizing agent in the absence of a diatomaceous filter-aid, at a sufliciently elevated temperature for a time sufficient to reduce the water content thereof to less than about 0.1%, without cracking said oil, and subsequently washing the dehydrated oil, and drying the Washed dehydrated oil.

EUGENE E. LANGAN.

NORMAN E. LEMMON.

FREDERICK W. SCHUESSLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,240,792 Dunham Sept. 18, 1917 1,761,328 Chappell June 3, 1930 1,964,953 Lazar July 3, 1934 2,187,883 Lemmon Jan. 23, 1940 2,294,884 Archibald Sept. 8, 1942 2,321,290 Giraitis June 8, 1943 2,327,504 Cohen Aug. 24, 1943 

